Defoaming mechanism of defoaming agent
Bubbles and foam often accompany people’s life and production. Sometimes we need to use them, such as flotation, fire extinguishing, dust removal, washing, making foam ceramics and plastics, etc.; sometimes we need to eliminate them, such as fermentation, coating, papermaking, printing and dyeing, eliminating flatulence in body organs, boiler water, wastewater treatment and prism (or glass) manufacturing, etc.
The so-called “bubble” or “gas bubble” refers to the presence of insoluble gas in liquid or solid, or in independent bubbles surrounded by their thin films. The accumulation state of many bubbles gathered together and separated from each other by thin films is called foam. Bubbles are a dispersed system with gas/liquid, gas/solid, and gas/liquid/solid interfaces. The latter is commonly seen in bubbles in mineral processing and oil field systems.
Generally speaking, pure water and pure surfactants do not foam because their surfaces and interiors are uniform and it is difficult to form an elastic film. Even if it is formed, it is unstable and will disappear instantly. However, in the presence of surfactants in the solution, after the bubbles are formed, due to the action of intermolecular forces, the hydrophilic and hydrophobic groups in the molecules are adsorbed by the bubble wall to form a regular arrangement, with the hydrophilic groups facing the water phase and the hydrophobic groups facing the inside of the bubble, thus forming an elastic film on the bubble interface, which is very stable and not easy to break under normal conditions. The stability of the foam is related to factors such as surface viscosity and elasticity, electrical repulsion, movement of the surface film, temperature, and evaporation.
Furthermore, bubbles are inversely related to the surface tension of liquids. The smaller the tension, the easier it is to foam. In life and production, the appearance of bubbles sometimes brings a lot of inconvenience to people, so defoaming is necessary. Any factor that can destroy the stability of foam can be used for defoaming. Defoaming covers two factors: “foam suppression” and “foam breaking”. Silicone defoaming agent has this function. It can reduce the surface tension of water, solution, suspension, etc., prevent the formation of foam, or reduce the original foam, and usually has a selective effect. Generally, physical defoaming methods are difficult to defoam instantly, while chemical and interfacial defoaming are very fast, convenient and efficient. In summary, defoaming agent refers to an agent with chemical and interfacial chemical defoaming effects.
As defoamers, there are low-carbon alcohols, mineral oils, organic polar compounds and silicone resins. They are in the form of oil type, solution type, emulsion type and foam type. As defoamers, they all have the characteristics of strong defoaming power, chemical stability, physiological inertness, heat resistance, oxygen resistance, corrosion resistance, gas dissolution, air permeability, easy diffusion, easy penetration, difficult to dissolve in the defoaming system, no physical and chemical effects, small amount of defoamer, high efficiency, etc.
There are many varieties of defoamers with a wide range of uses. The process of “foam suppression” and “foam breaking” of defoamers is as follows: when the defoamer is added to the system, its molecules are randomly and widely distributed on the surface of the liquid, inhibiting the formation of an elastic film, that is, terminating the generation of foam. When a large amount of foam is generated in the system, the defoamer is added, and its molecules are immediately spread on the surface of the foam, spreading rapidly to form a very thin double film layer, which further diffuses, penetrates, and invades in layers, thereby replacing the original thin film wall of the foam. Due to its low surface tension, it flows to the liquid with high surface tension that produces the foam. In this way, the defoamer molecules with low surface tension continue to diffuse and penetrate at the gas-liquid interface, causing its film wall to become thinner rapidly. At the same time, the foam is strongly pulled by the surrounding film layer with high surface tension, which causes an imbalance in stress around the foam, thereby causing it to “break”.
The defoamer molecules that are insoluble in the system will re-enter the surface of another foam film, and this process will be repeated until all the foams are destroyed. In industrial production, a lot of foams that are difficult to produce will be produced. At this time, defoaming is needed. There are many types of defoamers, including water-based defoamers and oil-based defoamers.
Recent research on defoamers has mainly focused on compound defoamers such as the compounding of organosilicon compounds and surfactants, the compounding of polyethers and organosilicones, and the compounding of water-soluble or oil-soluble polyethers and silicon-containing polyethers. Compounding is one of the development trends of defoamers. As far as current defoamers are concerned, polyether and organosilicon defoamers have the best performance, and research on the modification and development of new varieties of these two types of defoamers is also relatively active.
